A magnetron is a transducer. When supplied with a high supply voltage of about 1000 volts, the magnetron produces electromagnetic waves radiating at very high frequency. This radiation is advantageously used to cause agitation in the molecules of a solid or a liquid substance. The magnetron is the principal device for microwave ovens, which uses the principle of thermal agitation to cook and heat food. These microwave ovens are designed particularly for domestic use. Since domestic electrical appliances are supplied with low voltage, it is necessary to provide a power supply device for the magnetron. In Europe, for example, an AC voltage has an amplitude of 220 volts at a frequency of 50 Hz.
There are known power supply devices comprising a resonant transformer having a controlled switch at the primary winding of the transformer. As a result of the controlled switch, the resonant transformer converts a low supply voltage available at the primary winding into a high supply voltage for delivery to the terminals of the load. The high supply voltage is available at the secondary winding of the transformer.
The primary winding of the transformer has filtering means with a resonant frequency equal to the excitation frequency of the transformer. The switch is controlled by a control signal. One parameter of this control signal is set to servo-control the quantity of energy transmitted to the secondary winding, i.e., the power supplied to the load. This parameter may be a frequency, a cyclical ratio or any other variable that can be controlled in a determinable way.
In normal operation, the magnetron absorbs power of about 1500 watts. The magnetron requires a high supply voltage that can vary between 800 and 1200 volts, with a typical mean value of about 1000 volts. The mean current is about 8 amperes, with excess voltages requiring a current of up to 40 A.
To reduce the size of the transformer of the power supply device, the windings of the transformer are made with copper wire. However, copper is becoming an increasingly costly material. Furthermore, the transformer is still too bulky to produce even more compact microwave ovens. However, the reduction in the size of the transformer is limited by the need to have available a mass of copper that is sufficient to dissipate the heat generated, especially as a result of the losses resulting from the saturation of the magnetic material of the transformer.